Method and composition for chemically polishing metals



3,457,107 METHOD AND COMPOSITHQN FOR CHEMICALLY POLEHING METALS FloydLouis Michelson, Chicago, and Eugene Frank Maisel, Palatine, Ill.,assignors to The Diversey Corporation, Chicago, llll., a corporation ofIllinois No Drawing. Filed July 20, 1965, Ser. No. 473,504 Int. Cl. BOSb3/08, 3/04 US. Cl. 1343 Claims ABSTRACT OF THE DISCLOSURE Compositionsand processes for chemically polishing stainless steel. The stainlesssteel is first treated with an aqueous alkaline oxidizing solution, suchas a sodium hydroxide-sodium permanganate solution, to condition themetal surface. The stainless steel is then treated with an acid brightdip solution containing hydrochloric, nitric and phosphoric acids and asmall amount of specific surfactants.

This invention relates to a method and a composition for chemicallypolishing metals. More particularly, the invention relates to a methodof chemically polishing a stainless steel surface having an oxidecoating thereon and to a composition useful in performing the method.

Methods for polishing and brightening stainless steel surfaces includemechanical polishing and bufling, electro-polishing, and chemicalpolishing. Mechanical polishing involves extensive handling of the Work,resulting in high labor costs, and often cannot be performed because ofthe intricate form and nature of the work. Electropolishing oftenproduces satisfactory results, but expensive equipment and largequantities of electrical energy are required. Prior chemical polishingmethods in some cases produce a grainy or satiny surface as contrastedto a polished surface and in other cases are relatively sensitive tochanges in the concentration of the materials employed,

so that they are diflicult to work with. In addition, the I materialsare employed in relatively high concentrations, resulting in high dragout losses, i.e., losses due to material remaining on the articlesremoved from the polishing bath, which is lost or becomes a contaminantin subsequent treating operations. Prior chemical polishing methods alsohave a tendency to remove unduly large quantities of metal from thearticles, thus excessively altering their dimensions.

During the fabrication of articles made of stainless steel, theyfrequently are welded, brazed or subjected to other heat treatment whichproduces a heat scale. This scale is unsightly and tends to aggravatecorrosion of the article, and consequently it must be removed.

US. Patent No. 3,072,515 discloses a method and composition fordescaling and chemically polishing metals, particularly stainless steel.The metal surface is contacted with an aqueous solution of hydrochloricacid, nitric acid, and an additive having a polyoxyethylene chain in itsmolecule, as more particularly described in the patent. The solution mayalso contain phosphoric acid to enhance the action of the reactants. Themetal surface is polished to a smooth, near-mirror finish whiledissolution of the base metal and drag out losses are minimized.

It has now been discovered in accordance with the present invention thatchemical polishing employing the solution of the foregoing patent may beimproved and chemical polishing also may be effected with othersolutions by subjecting a metal surface to a pretreatment whichconditions or activates the surface. In particular, the metal surface iscontacted with an aqueous alkaline oxidizing solution to condition thesurface and prepare it for oxide removal and subsequent chemicalpolishing of the surface. The polishing action according to theabovernentioned patent is improved, and other polishing solutions may beemployed which previously failed to produce an acceptable polishedsurface.

The pretreated metal surface is then contacted with an aqueous solutioncontaining hydrochloric acid, nitric acid, and a surfactant. Thesurfactant may constitute a compound having a polyoxyethylene chain inits molecule, as defined in the patent, or it may constitute one of anadditional class of compounds as described hereinafter. The solutionalso may contain phosphoric acid, which enhances the action of thesolution, apparently stabilizing the solution and inhibiting pitting ofthe metal surface.

In this manner, metal surfaces, especially stainless steel surfaces, arechemically polished to remove scale and oxides and give a surface havinga smooth, near-mirror finish. Reference to stainless steel herein refersto the alloys of principally iron, chromium, and nickel, or of iron andchromium, together with minor constituents.

In addition to producing bright polished surfaces on metals such asstainless steel, the invention is advantageous in that the solutionsrequire only relatively low cost materials which are employed inrelatively low concentrations, thereby minimizing drag out losses. Onlya relatively small amount of base metal is removed in the process of theinvention, so that changes in the dimensions of the finished articlesare minimized.

The metal surfaces to be polished preferably are subjected to aconventional preliminary cleaning to remove oil, grease, drawingcompounds and the like. The clean surfaces then are contacted with anaqueous alkaline oxidizing solution which preferably contains an alkalimetal permanganate such as potassium or sodium permanganate. Thesolution preferably contains about 24% by weight of the permanganate. Itis also preferred that the solution be highly caustic. The desiredcausticity preferably is provided by a strong base, more preferably analkali metal hydroxide such as sodium or potassium hydroxide. The basemay be employed in a concentration of about 510% by weight. A watersoftener also may be included, such as an alkali metal carbonate,preferably sodium or potassium carbonate. The softener is employed in aminor effective amount, it being preferred to employ a carbonate in aproportion of about (LS-1% by weight of the solution.

The metal is contacted with the oxidizing solution at an elevatedtemperature and for a period of time suflicient to condition the metalsurface to prepare it for subsequent chemical polishing. It is preferredthat the temperature of the solution be in the range of about F. to theboiling point. The metal is maintained in contact with the solution fora period of time in the range of about A to 1 /2 hours, the time varyinginversely with the temperature. The resulting pretreated metalpreferably is Washed with an acid solution to neutralize causticremaining on the metal and then rinsed, following which the metal ischemically polished.

The metal is contacted with an aqueous polishing solution preferablycontaining about 1-10% by weight of hydrochloric acid, about 1-8% byweight of nitric acid, and about 0-60% by Weight of phosphoric acid, andadvisably also containing about ODS-20% by weight of a surfactant. It isfurther preferred that the solution contain about 28% of hydrochloricacid, about 2-6% of nitric acid, about 1535% of phosphoric acid, andabout 0.215% of surfactant.

The surfactant may be one of the compounds described in the aboveidentified Patent No. 3,072,515. These surfactants are (l) condensationproducts of 1 mole of phenol with about -30 moles of ethylene oxide, (2)condensation products of 1 mole of an alkyl phenol having up to about 15carbon atoms in the alkyl group with about 5-30 moles of ethylene oxide,(3) condensation products of 1 mole of an alkyl amine having about -20carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide,(4) condensation products of 1 mole of an aliphatic alcohol having about10-20 carbon atoms in the alkyl group with about 5-50 moles of ethyleneoxide, (5) condensation products of 1 mole of a polypropylene glycolcontaining about 10-50 propylene oxide units with about 4-150 moles ofethylene oxide, and (6) mixtures thereof.

Alternatively, other surfactants can be employed which contain analiphatic chain of 6 to 20 carbon atoms. A preferred group ofsurfactants includes the cationic aliphatic, araliphatic andheterocyclic amines, non-ionic and anionic aliphatic acid amides,non-ionic aliphatic acid partial esters of polyhydric alcohols and theirpolyoxyethylene ethers, anionic aliphatic sulfates, anionic aliphaticesters of sulfonated aliphatic acids, anionic aliphatic aryl polyethersulfonates, and anionic aliphatic phosphates.

The cationic aliphatic, araliphatic and heterocyclic amines are primary,secondary, tertiary and quaternary amines containing at least onealiphatic chain of 6 to 20 carbon atoms, which may be a straight orbranched chain. Representative compounds include the mono-, diandtrin-alkyl fatty amines. Exemplary compounds include the primary,secondary and tertiary fatty amines identified by the trade name Armeen.

Other compounds include the alkyl and the aralkyl quaternary ammoniumsalts. Preferred compounds of this type contain one alkyl group havingfrom 8 to 16 carbon atoms, two alkyl groups having from 1 to 6 carbonatoms, and an aralkyl group having from 7 to 10 carbon atoms, such asalkyl dimethyl ethylbenzyl ammonium chloride identified by the tradename Onyx BTC 471.

The heterocyclic amines include the substituted glyoxalidines and thesubstituted oxazolines, employed as their acid addition salts.Representative compounds include l-hydroxyethyl-2-heptadecenylglyoxalidine identified by the trade name Alro Amine O, and asubstituted oxazoline identified by the trade name Alkaterge C.

The non-ionic aliphatic acid amides include the amides of preferablylower aliphatic amines such as amino-ethyl ethanolamine anddiethanolamine and fatty acids having a straight or branched aliphaticchain of 6 to 20 carbon atoms. Representative compounds includeaminoethyl ethanolamine fatty acid amides identified by the trade nameNopcogen RP and diethanolamine fatty acid amide identified by the tradename Ninol, 1001.

The anionic aliphatic acid amides includes the amides of 6-20 carbonatom straight or branched chain aliphatic acids with preferably loweraliphatic aminosulfonic and amino-carboxylic acids. The amino grouppreferably is also substituted with a 1-6 carbon atom alkyl group.Representative compounds include sodium N-cyclohexyl-N-palmitoyl-taurate identified by the trade name Igepon (IN-42, sodiumN-methyl-N-oleoyl-taurate identified by the trade name Igepon T-33, andN-meth.yl-Noleoyl glycine identified by the trade name Sarkosyl O.

The non-ionic aliphatic acid partial esters of polyhydric alcohols andtheir polyoxyethylene ethers include the 6-20 carbon atom straight orbranched chain aliphatic acid partial esters of sorbitol, propyleneglycol, and glycerol, and their polyoxyethylene ethers. Representativecompounds are sorbitan monooleate identified by the trade name Span 80and polyoxyethylene sorbitan monooleate, called Tween 80.

The anionic aliphatic sulfates includes the 6-20 carbon atom straight orbranched chain alkyl sulfates or sulfate esters. A representativecompound is sodium lauryl sulfate identified by the trade name DuponolC.

The anionic aliphatic esters and amides of sulfonated dicarboxylic acidsinclude the 6-20 carbon atom straight or branched alkyl esters ofsulfonated lower dicarboxylic acids. A representative compound is sodiumsulfosuccinic acid dioctyl ester identified by the trade name Aerosol OTand disodium N-octadecylsulfosuccinamate identified by the trade nameAerosol 18.

The anionic aliphatic aryl polyether sulfonates include the 6-20 carbonatoms straight or branched chain alkyl substituted aryl polyethersulfonates. A representative compound is sodium octyl phenoxy polyethoxysulfonate identified by the trade name Triton X-200.

The anionic aliphatic phosphates includes the 6-20 carbon atom straightor branched chain alkyl monoand polyphosphates containing up to 8phosphate radicals. Representative compounds include (Z-ethylhexyl) -Na(P O identified by the trade name Victawet 35B and (capryl) Na (P Oidentified by the trade name Victawet 58B and monophosphates such aslauryl ester of ortho phosphoric acid.

Additional surfactants which may be employed include the anionicfluorinated aliphatic compounds such as Howchemical FC- and theamphoteric surfactants such as the ethoxylated sodium salt Triton QS-lS.

In the preferred practice of the invention, a concentrate is providedfor handling and storage purposes, and the polishing solution may bemade up from the concentrate. A preferred concentrate contains about6-9% by weight of hydrochloric acid, about 25-65% by weight ofphosphoric acid, about 1-3% by weight of a surfactant, and the remainderwater. The above Patent No. 3,072,515 discloses concentrates of thistype containing a compound having a polyoxyethylene chain in itsmolecule. The present invention provides concentrates useful inpracticing the invention which include a surfactant containing analiphatic chain of 6-20 carbon atoms, as described above. A preferredspecific concentrate contains about 8% by weight of hydrochloric acid,about 60% by weight of phosphoric acid, about 2.6% of the surfactant,and the remainder water. A polishing solution is compounded by addingnitric acid and water to a concentrate to provide a solution containinghydrochloric acid, nitric acid, phosphoric acid, and a surfactant in theproportions described above.

The metal to be polished is contacted with the polishing solution in ahath made up of the solution, at an elevated temperature and for aperiod of time sufficient to produce a bright polished surface. The bathis maintained at a temperature preferably in the range of about -200 F.,more preferably l60-190 F. The time required to produce a brightpolished surface varies depending upon the temperature of the bath, thecomposition of the solution, the type of metal, and the condition of themetal surface. Ordinarily, the time required is about 5 to 20 minutes ata temperature in the range of about 190 F., with the time decreasing atincreasing temperatures, and increasing at decreasing temperatures.Following the polishing treatment, the metal is rinsed, at which time itis found to have the desired polished surface.

The following examples are illustrative of the invention. The inventionis not limited to the examples or to the materials, proportions,conditions and procedures set forth therein. The acid proportions arebased on 100% acid except Where otherwise indicated.

Example 1 Panels of 24 gauge stainless steel, Type 302 having a 2B(matte) finish that had acquired a thin oxide coating were cleaned toremove oil, grease and the like by immersing them for 10 minutes at F.in a solution of the following composition in water, the compositionbeing employed in a concentration of 6 ounces per gallon of totalsolution:

Proportion, per- Material: cent by weight Sodium hydroxide 50 Sodiumcarbonate 47 Sodium oleate 3 The panels were removed from the solutionand rinsed with tap water.

The panels were immersed for 30 minutes in the following alkalineoxidizing solution at 200 F., to remove the surface oxides:

Proportion, per- Material: cent by weight Sodium hydroxide 7.9 Potassiumpermanganate 3.2 Sodium carbonate, anhydrous 0.7 Water 88.2

The panels were removed from the oxidizing solution and rinsed with tapwater.

The panels were immersed for 5 minutes in a solution of the followingcomposition diluted with 3 parts by volume of water and maintained at 80F., to neutralize any caustic remaining on the panels:

Proportion, per- Material: cent by weight Phosphoric acid, 75% conc.Xylene sulfonic acid 5 Octyl phenoxy polyethoxy ethanol containing about11-13 mols of ethylene oxide 5 Sodium dodecyl diphenyl ether disulfonate2 Water 83 The panels were removed from the oxidizing solution andrinsed with tap water.

The panels then were immersed for minutes in the following polishingsolution maintained at 17 6-180 F.:

Proportion, per- Material: cent by weight Hydrochloric acid 3 Nitricacid 3 Phosphoric acid 24 Aminoethyl ethanolarnine fatty acid amide 1 1Water Balance 1 Nopcogen RP.

The panels were withdrawn from the bath and rinsed with tap water. Theywere found to have a bright, smooth near-mirror finish. Without thepretreatment using the oxidizing permanganate solution the panels aresubstantially less bright and lack the mirror finish.

When the foregoing procedure was repeated with the omission of theaminoethyl ethanolamine fatty acid amide from the polishing bath, nobrightening or polishing of the panels was obtained. In addition,non-uniform etching of the panels was observed.

Example 2 The procedure of Example 1 was repeated, with the differencethat 5% instead of 3% of hydrochloric acid was employed in the polishingsolution. Equivalent results were obtained.

Example 3 The procedure of Example 1 was repeated, with the differencethat 5% instead of 3% nitric acid was employed in the polishingsolution. Equivalent results were obtained.

Example 4 Example 1 was repeated, employing 15% instead of 24% ofphosphoric acid in the polishing solution, and employing 1% of amonoalkyl amine having 68 carbons in the alkyl group (Armeen-8) in placeof the aminoethyl ethanolamine fatty acid amide in the polishingsolution. The panels were immersed in the polishing solution forminutes. Equivalent results were obtained.

Example 5 The procedure of Example 1 was repeated, employing differentsurfactants in the polishing solution. A bright, smooth, near-mirrorfinish was obtained in each case with respective polishing solutionscontaining 1% by weight of the following surfactants singly or incombination when compatible:

l-hydroxyethyl-2-heptadecenyl glyoxalidine salt (Alro Amine O).

Substituted oxazoline tertiary amine salt (Alkaterge C).

Polyoxyethylene sorbitol oleate (Atlas G-1186).

Diethanolamine fatty acid amide (Ninol 1001).

Sodium lauryl sulfate (Duponol C).

Sodium sulfosuccinic acid dioctyl ester (Aerosol OT).

N-methyl-N-oleyl glycine (Sarkosyl O).

(Capryl) -Na (P O (Victawet 58B).

Fluorinated anionic surfactant (Florochemical FC-95).

Sodium salt of an ethoxylated amphoteric surfactant (Triton QS-15 In theabsence of pretreatment with oxidizing solution the finish of the panelsis substantially less bright.

Example 6 The procedure of Example 1 was repeated with panels of 24gauge stainless steel, Type 316 that had acquired a thin oxide coating.The following surfactants can be employed singly or in combination whencompatible in respective polishing solutions at a concentration of 1% byweight in each solution, and a bright, smooth nearmirror finish isproduced in each case.

Tri-n-alkyl tertairy amines such as Armeen DMCD which is a trialkylaminein which one alkyl group contains 818 carbons and the others are methylgroups and Armeen MZHT which is methyl dehydrogenated tallowamine.

Di-n-alkyl secondary amines such as Armeen 20 which has alkyls having618 carbon atoms.

n-Alkyl primaryamines such as Armeen 8 which has an alkyl having 6-10carbons.

Quaternary ammonium chloride having two methyl groups, one ethylbenzylgroup and one alkyl group having 6 to 20 carbons such as Onyx BTC 471which has 12-18 carbon atoms in the long chain alkyl group.

1-hydroxyethyl-2-h:ptadecenyl glyoxalidine salt (Alro Amine O).

Substituted oxazoline tertiary amine salts such as Alkaterge C which is2 heptadecyl 5 methyl 5 hydroxymethyl oxazoline.

Polyoxyethylene sorbitol oleate (Atlas G-l186).

Polyoxyethylene sorbitan oleate (Tween Diethanolamine capric acid amide(Ninol 1001).

Sodium lauryl sulfate (Duponol C).

Sodium N-methyl-N-oleyl-taurate (Igepon T33).

Sodium sulfosuccinic acid dioctyl ester (Aerosol OT).

N-methyl-N-oleyl glycine (Sarkosyl O).

(Capryl) -Na (P O (Victawet 58B).

Fluorinated anionic surfactant (Florochemical FC-).

Sodium salt of an ethoxylated amphoteric surfactant (Triton QS-lS).

Sorbitan monooleate (Span80).

Sodium alkyl aryl polyether sulfonate (Triton X-200).

1 (2 sodium acetato) 1 (2 sodium ethylato) 2- undecyl4,5-dihydroimidazolium hydroxide (Miranol M).

When the pretreatment with oxidizing solution is omitted the panels aresubstantially less bright and the finish is not near-mirror like.

Example 7 Pipe couplings of forged stainless steel, Type 304 and Type316 having a black surface coating of heat scale from prior heattreatment were treated according to the method of Example 1. Thecouplings were immersed in the polishing solution for about 10 to 20minutes at a temperature of about 190 F. The couplings came out brightand free of scale.

.7 Example 8 An article was prepared which consisted of a piece ofstainless steel, Type 302 and pieces of mild steel copper, and brassattached to the stainless steel by silver solder. The soldering produceda heavy, blue-black heat scale on the stainless steel. The article wastreated by the method of Example 1, immersing it in the polishingsolution for minutes at about 190 F. A clean and bright surface wasproduced on the stainless steel, The copper and brass were clean. Themild steel had evidence of a light attack. There was practically noattack. on the silver solder.

Example 9 Welded stainless steel, Type 302 was cleaned in an aqueoussolution containing 6 oz./gal. of the composi tion:

Proportion, percent Material: by weight Sodium hydroxide 50 Sodiumcarbonate 47 Sodium oleate 3 For the cleaning, the solution was used at160 F. for 10 minutes. Then the stainless steel was rinsed with waterand pretreated with an aqueous oxidizing solution containing 0.5 or 1.0lb./ gal. of a mixture of the following:

Proportion, percent Material: by weight Sodium hydroxide 65 Potassiumpermanganate 27 Sodium carbonate 8 Material: by weight Phosphoric acid24 Hydrochloric acid 3 Nitric acid 3 Alkyl aryl polyether alcohol(Triton X-100) 1 Water 69 The solution was used at 170 F. for 10 minutesfollowed by a water rinse and drying.

The stainless steel samples pretreated with the oxidizing solutionscontaining 0.5 lb./gal. and 1.0 lb./gal. of the materials specifiedabove gave uniform polished surfaces after the full process wascompleted as described. The same result was obtained using an oxidizingsolution containing 1.0 lb./ gal. of the specified materials for a 60minute pretreatment followed by the further specified treatments.However, a control which was not pretreated with an oxidized solutionbut which was treated as otherwise described in this example had theweld seam still scaled, and a very matte band 4 inch thick and /2 inchfrom the weld seam developed over the polished surface.

The process was repeated except that the Triton X100 in the polishingsolution was increased to with a corresponding reduction in thepercentage of water. Readings of 24% and 53% absolute specularreflectance respectively were obtained before and after polishing usingthe cycle of this example. (The significance of specular reflectancevalues is explained in Example 10.)

Example 10 The procedure of Example 9 was followed in polishingheat-treat scaled stainless steel panels using oxidizing solutionconcentrations and treatment times as indicated in the following TableA:

1 Ingredients as in Example 9. 2 Control stainless steel panel beforetreatment read 4% absolute specular reflect-once.

Specular reflectance is measured with an apparatus that operates on thesame principle as the well-known light meter used in photography, i.e.,reflected light is recorded on a scale in the instrument. The instrumentis first calibrated by adjusting the indicator to record a maximum of100% for a given amount of reflected light from a highly polishedsurface such as a mirror. It is also adjusted to record 5.6% reflectancefrom a panel of black glass. Table A shows that much higher specularreflectance is obtained when the permanganate oxidizing solution is usedthan when it is omitted from the polishing process, it being understoodthat the treatments with the polishing solution are of equal length.

Example 11 A Type 302 stainless steel lot found to be diflicult topolish because of heavy scale was treated as in Example 9, except thatthe Triton X-100 in the polish solution was replaced by an equal amountof Aliquat 4 (N-fatty trimethyl quaternary ammonium chloride) or FC-(fluorinated anionic surfactant). The results are found in Table B andshow that superior results are obtained when the permanganate oxidizingpretreatment solution is used.

TABLE B Percent absolute specular reflectance 2 oxidizing solutionconcentration 1 Time (min) Aliquat 4 IFS-95 Control 32 37 1 lb./gal 3038 42 1 Ingredients as in Example 9.

2 Control stainless steel panel before treatment read 24% absoluetSpecular reflectance.

Example 12 Type 304 stainless steel was scaled by placing panels on an800 F. plate temperature hot plate for 1 .and 2 hours, then polished asin Example 9. The results obtained are found in Table C and show theeffect the permanganate oxidizing pretreatment solution has when used ondifiicult heat scales.

TABLE 0 Percent absolute specular reflectance After After Beforepolishing polishing no polishing oxidizer in oxidizer in with scalecycle cycle 1 hr. heat scale 21 57% 4 2 hr. heat scale 16 59 1 Example13 Operating at the acid ratio and the cycle as in Example 9, the highmolecular weight surfactant in the polishing solution was replaced withan unsaturated alcohol of the propynol and butynediol types. The resultsobtained are given in Table D, and show the effect the preferred acidratio has on polishing.

TABLE D Percent absolute specular reflectance Before polishing Afterpolishing 2 propyn-l-ol 23 54 2 butyne-L4 diol 22% 5 The processed panelsurface had a grey cast. However, the unsaturated alcohols such aspropynol and butynediol may be used to obtain brightening using thepreferred acid ratio.

It will be apparent that various changes and modificatiors may be madein the method and composition of the invention within its spirit andscope. It is intended that such changes and modifications be includedwithin the scope of the appended claims.

What is claimed is:

1. A method of chemically polishing a stainless steel surface having anoxide coating thereon which comprises contacting said surface with anaqueous alkaline oxidizing solution at an elevated temperature and for aperiod of time sufiicient to condition the surface of the stainlesssteel for subsequent chemical polishing of said surface, and thereaftercontacting said surface with a chemical polishing aqueous solutioncontaining about 1l0% by weight of hydrochloric acid, about 18% byweight of nitric acid, about 0-60% by weight of phosphoric acid, andabout 0.05% by weight of a surfactant selected from the group consistingof cationic aliphatic, araliphatic and heterocyclic amines, non-ionicand anionic aliphatic acid amides, non-ionic aliphatic acid partialesters of polyhydric alcohols and their polyoxyethylene ethers, anionicaliphatic sulfates, anionic aliphatic esters of sulfonated aliphaticacids, anionic aliphatic aryl polyether sulfonates, and anionicaliphatic phosphates, at an elevated temperature and for a period oftime sufficient to produce a bright polished surface.

2. The method according to claim 1 in which the alkaline oxidizingsolution contains an alkali metal permanganate.

3. A method of chemically polishing a stainless steel surface having anoxide coating thereon which comprises contacting said surface with anaqueous alkaline oxidizing solution at an elevated temperature and for aperiod of time suflicient to condition thesurface of the stainless steelfor subsequent chemical polishing of said surface, and thereaftercontacting said surface with a chemical polishing aqueous solutioncontaining about 28% by weight of hydrochloric acid, about 26% by weightof nitric acid, about 060% by Weight of phosphoric acid, and about02-15% by weight of an aminoethyl ethanolamine amide of a fatty acidhaving an aliphatic chain of 6-20 carbon atoms, at an elevatedtemperature and for a period of time sufficient to produce a brightpolished surface.

4. The method according to claim 3 in which the alkaline oxidizingsolution contains an alkali metal permanganate.

5. A method of chemically polishing a stainless steel surface having anoxide coating thereon which comprises contacting said surface with anaqueous alkaline oxidizing solution at an elevated temperature and for aperiod of time suflicient to condition the surface of the stainlesssteel for subsequent chemical polishing of said surface, and thereaftercontacting said surface with a chemical polishing aqueous solutioncontaining about 28% by Weight of hydrochloric acid, about 2-6% byweight of nitric acid, about 060% by weight of phosphoric acid, andabout 02-15% by weight of a salt of an aliphatic amine having at leastone aliphatic chain of 6-20 carbon atoms, at an elevated temperature andfor a period of time sufficient to produce a bright polished surface.

6. The method according to claim 5 in which the alkaline oxidizingsolution contains an alkali metal permanganate.

7. A method of chemically polishing a stainless steel surface having anoxide coating thereon which comprises cleaning the surface with acaustic solution to remove oil, grease and the like from the surface,rinsing the surface with water, contacting said surface with an alkalineoxidizing solution containing an alkali metal permanganate andmaintaining said solution in contact with said surface at a temperatureof about 150 F. to the boiling point for a period of time sufficient tocondition the surface of the stainless steel for subsequent chemicalpolishing of the surface, rinsing the surface with water, neutralizingthe surface with an aqueous acidic solution, rinsing the surface withwater, contacting said surface with a chemical polishing aqueoussolution containing about 110% by weight of hydrochloric acid, about 18%by weight of nitric acid, about 0-60% by weight of phosphoric acid andabout ODS-20% by weight of a surfactant selected from the groupconsisting of cationic aliphatic, araliphatic and heterocyclic amines,non-ionic and anionic aliphatic acid amides, non-ionic aliphatic acidpartial esters of polyhydric alcohols and their polyoxyethylene ethers,anionic aliphatic sulfates, anionic aliphatic esters of sulfonatedaliphatic acids, anionic aliphatic aryl polyether sulfonates, andanionic aliphatic phosphates, at an elevated temperature and for aperiod of time sufficient to produce a bright polished surface, rinsingthe surface with water and drying the surface.

8. A bath which consists essentially of an aqueous solu- I tioncontaining about l10% by weight of hydrochloric acid, about l8% byweight of nitric acid, about O60% by weight of phosphoric acid, about0.0520% by weight of a surfactant containing an aliphatic chain of 620carbon atoms and selected from the group consisting of cationicaliphatic, araliphatic and heterocyclic amines, non-ionic and anionicaliphatic acid amides, non-ionic aliphatic acid partial esters ofpolyhydric alcohols and their polyoxyethylene ethers, anionic aliphaticsulfates, anionic aliphatic esters of sulfonated aliphatic acids,anionic aliphatic aryl polyether sulfonates, and anionic aliphaticphosphates, and the remainder water.

9. A concentrated mixture which consists essentially of about 69% byweight of hydrochloric acid, about 2565% by Weight of phosphoric acid,about l3% by weight of a surfactant containing an aliphatic chain of 6to 20 carbon atoms and selected from the group consisting of cationicaliphatic, araliphatic and heterocyclic amines, non-ionic and anionicaliphatic acid amides, nonionic aliphatic acid partial esters ofpolyhydric alcohols and their polyoxyethylene ethers, anionic aliphaticsulfates, anionic aliphatic esters of sulfonated aliphatic acids,anionic aryl polyether sulfonates, and anionic aliphatic phosphates, andthe remainder water.

10. A concentrated mixture which consists essentially of about 8% byweight of hydrochloric acid, about 60% by weight of phosphoric acid,about 2.6% by weight of aminoethyl ethanolamine amide of a fatty acidhaving 11 12 an aliphatic chain of 6 to 20 carbon atoms, and the3,125,475 3/1964 Livingston et a1. 25279.1 X remainder Water. 3,220,89911/1965 Leonard 25279.5

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